Method and apparatus for manufacturing wood pulp



Dec. 28,1926. 1,612,484

E. R. BARKER ET AL METHOD AND APPARATUS FOR MANUFACTURING WOOD PULP Filed May 15, 1926 by them" atty.

Patented Dec. 28, 1926.

UNITED STATES PATENT OFFICE.

ELLIOTT R. BARKER, OF ARLINGTON, AND FRANCIS J. DOOLEY, OF MEDFORD, MASSACHUSETTS.

METHOD AND APPARATUS FOR MANUFACTURING WOOD PULP.

Application filed May 15, 1926.

This invention relates to certain new and improved methods for the recovery ofheat and chemicals from sulphite digesters during the process of cooking wood chips to obtain pulp or fiber therefrom for use in the paper industry.

Heretofore sulphite pulp has been obtained from wood by cooking chips of the wood in a digester with a solution of calcium or magnesium sulphite, or both, and free sulphurous acid. These chemicals, at proper temperatures and pressures, render the intercellular matter soluble, thus freeing the fibers and leaving them in the form of ap proximately pure cellulose, in proper condi tion for use with other materials to make paper.

The cooking process, so called, is carried out in large cylindrical vessels known as.

digesters. These digesters are filled wholly, or in part, with chips of wood and the solution of chemicals called bisulphite liquor. A steam supply pipe is connectedto the bottom of the digesters. Relief pipes are connected at or near the top.

After the charge of chips and bisulphite liquor have been put into the digester and the cover fastened on, and the pipe connec tions made, steam is introduced through the bottom of the digester to raise the temperature and assist the solution and decomposition of the intercellular matter. I

In order to admit sufficient steam to produce the required temperature and to obtainuniform circulation and temperature throughout the mass'of chips and chemicals, a certain amount of bisulphite liquor with the sulphur dioxide as which has escaped from solutions must e released or allowed to pass out ofthe di'gesten. The matter thus passing out of the digester contains large amounts of valuable chemicals and heat, and the heat therein through the usual recovery process, is lost in the coolers through which the relief must-pass before it enters the reclaiming tanksortowers. p j

Itis the ob'ect of this invention to save facilitate the cooking process. I

The invention, therefore, resides in the improved method and apparatus for manu- ,facturing wood pulp hereinbefore described and particularly pointed out in the claims. 55

Referring to the drawings a large amount of the chemicals and the heat" contained therein in a manner f which will Serial No. 109,383.

Figure 1 is a front elevation of an apparatus for manufacturing wood pulp embodying our invention, the same being broken away to save space.

Fig. 2 is a plan view in detail of the digesters and piping which particularly embody -our invention.

Like numerals refer to like parts through out the several views of the drawings.

In the drawings, 5 and 6 are two digester tanks. 7 is a steam pipe which is connected by pipes 8 to the bottom of the digester 5 and by pipes 9 to the bottom of the digester 6. Check valves 10 and 11 are provided in the pipes 8 and 9 respectively, also shut-oil" valves 12 and 13 are provided in said pipes 8 and 9. Steam can thus be forced into the d igesters 5 and 6 which have been previously filled with Wood chips and a solution of calcium or magnesium bisulphite, or both, and free sulphurous acid.

Bisulphite liquor is supplied to the tank 6 by a pump 14 and electric motor 15 through pipes 16, 17 and 9. Bisulphite liquor is supplied to the tank 5 through pipes 16, 18, 19

and 8. The supply of bisulphite liquor may be cut ofl from the tank 6 by a valve 20 and from the tank 5' by a valve 21.

A relief'pipe 22 leads from the top of the digester tank 5 to a' main relief pipe 23 and in like manner the top of the digester tank 6 is connected by a relief pipe '24 tosaid main relief pipe 23. The main relief pipe 23 is furthermore connected'by branch pipes 25 and 26 to the digester tanks 5 and 6 respectively at points substantially below the tops of said tanks, but still in the upper region thereof. A valve 27 is interposed in the pipe 22 between the tank 5 and the pipe 23, and a's'imilar valve 28 is interposed in the pipe 24 between the tank Gand said pipe 23. Valves 29 'and 30 close the pipe 23 to the digester tanks "5 and 6 respectively. Other relief 'pipes'31 and 32 lead from the top of the digester tanks 5 and 6 respectively, and the passage of fluid through said pipes is controlled-by valves 33 and 34 respect-ively. v

'Th'e general'operati'on 0f the apparatus hereinbefore specifically described is as follows :Assuming the digester tank 5 to be operating in the usual manner 'to'cook the wood chlps, the digester 6 is then supplied with chips in the usual well-known'm'anner,

' the level of the said chips in said digester 6 covering the point where the pipe 26 dis-.

charges into said digester.

The digester tank 6 is then supplied from the bottom with bisulphite liquor to'a point adjacent the level at which the pipe 26 discharges into the digester tank 6. A less volume of bisulphite liquor is thus put into the digester tank 6 from the bottom than has been the previous practice, thus requiring less steam to obtain the required cooking temperature than has been the case where the digesters have been more nearly filled with bisulphite liquor.

Assuming the material in the digester 5 to have advanced in the cooking process to the point where it is desirable to allow the bisulphite liquor with the sulphur dioxide gas which has escaped from the solution to pass out of the digester 5, then the valve 27 being opened and the valves 28, 29, 33 and 34 closed, and the valve opened, heated bisulphite liquor and sulphurous acid will pass from the digester tank 5 through the pipes 22,23 and 26 into the digester tank 6 due to the pressure in the digester tank 5 being substantially in excess of the pressure at that time in the digester tank 6. As a matter of fact, in practice, the pressure in the tank 5 at the time when the valves 27 and 30 are opened is about fifty pounds, while the pressure in the digester tank 6 is zero. While the bisulphite liquor and the sulphur dioxide gas are passing from the digester tank 5 to the digester tank 6, thepressure in the tank 5 is gradually increased by the steam admitted to the tank 5 until it arrives at a pressure of from sixty to seventy pounds, and during this time the pressure in the digester tank 6 is always substantially lower than the pressure in the tank 5.

When the digester tank 6 has been thus filled with chips and bisulphite liquor to the desired point, the cover is bolted on, the valves 28 and 34; are closed and steam is supplied through the bottom of the digester 6 through the pipe 9 from the pipe 7.

When the volume of the relief and steam has increased the pressure in the digester 6v so as to retard the cooking process in the digester 5, the relief valve 34 for the digester 6 is opened and the gas and bisulphite liquor allowed to pass out of said digester, either to enter a third digester at less pressure than that in the digester 6, or allowed to flow to the coolers, reclaiming tanks or towers through the pipe'32.

It will be noted that the relief pipe 26 is connected to the tank 6 at a point substantially below the top thereof, it being understood that the pressure in the first digester tank 5 must be substantially more than that in the second digester tank 6 and that the relief will be admitted into the second (ligei'ter 6 at a point where. the hydrostatic head, due to the cooking liquor will not cause serious back pressure in the first digester tank 5.

It will be understood that several digester tanks can be used in a similar manner in series, the cooking process in the first tank being farther advanced than that in the second tank, and the cooking process in the second tank being farther advanced than that in the third tank, and so on throughout the series.

After the chips'in the first tank have been cooked by the process hereinbefore de' scribed, to produce sulphite pulp, the digester tank is emptied and then refilled with chips, and the process hereinbefore described is repeated, and so on throughout the series of digester tanks. By this rocess, large amounts of chemicals and-t e heat contained therein can be saved.

By properly manipulating the different valves it will be seen that the gas and liquor can pass from the digester tank 5 through the pipes 22, 23 and 26 to the digester'tank 6, or the heated gas and liquor may pass fromthe digester tank 5 through the pipe 31 and thence to the coolers or to other recovery apparatus.

It will also be seen that the process may be reversed and liquor and gas from the digester tank 6 can pass through the pipes 24, 23 and 25 into the digester'tank 5, or that such liquor and gas can pass from the tank 6 through the pipe 32 to suitable coolers, or to other recovery apparatus, all as may be desired to obtain the'results hereinbefore set forth.

\Ve claimz' 1. A step in the process of manufacturing wood pulp which consists in conveying the excess bisulphite liquor and sulphur dioxide gas from one digester to a second digester at a point substantially removed from the top and bottom of said second digester.

2. A step in the process of manufacturing wood pulp which consists in conveying the excess bisulphite liquor and sulphur dioxide gas from one digester to a second digester at a point substantially removed from the top and bottom of said second digester, the cooking process in the first-named digester being farther advanced than in the secondnamed digester.

3. A stepin the process of manufacturing wood pulp which consists in conveying the the excess bisulphite liquor and sulphur dioxide gas consecutively. from one to another of a series of digesters during the cooking process the point at which the said excess bisulphite liquor and sulphur dioxide gas are delivered 'to each digester being substantially removed from the top and bottom of said digester, the cooking process in the different digesters being at relatively different stages of advancement, and the ex cess bisulphite liquor and sulphur dioxide lOO gas oeing conveyed in each case from a digester at a more advanced stage to a digester in a less advanced stage.

4:- A step in the process of manufacturing Wood pulp which consists in conveying the excess bisulphite liquor and sulphur dioxide gas from the upper part of one digester to another digester at a relatively lower point therein and at a substantial distance from the bottom thereof, the cooking process in the first-named digester being farther advanced than in the second-named digester.

5. The process of manufacturing wood pulp which consists in mixing wood chips with bisulphite liquor in a digester and forcing steam into the bottom of said digester, and after the cooking process has proceeded for a predetermined time conveying the excess bisulph ite liquor and sulphur dioxide gas from one digester to a second digester at a point adjacentthe level of the bisulphite liquor in said second digester and the cooking process in the first-named digester being farther advanced than in the second-named digester.

6. The process of manufacturing wood pulp which consists in mixing wood chips with bisulphite liquor in a digest-er and forcing steam into the bottom of said digester, and after the cooking process has pro needed for a predetermined time conveying the excess bisulphite liquor and sulphur dioxide gas from the upper part of said digester to. a second digester at a" relatively lower point therein, the second digester hav-. ing been, at this predetermined time, wholly or partly filled with chips and with bisul: phite liquor to a point adjacent to the point where the heated bisulphite liquor from the first digester is entering the second digester and supplying steam to the second digester through the bottom thereof.

7 The process of manufacturing wood ulp which consists in mixing wood chips with bisulphite liquor in a digester and "ing been, at this predetermined time,

forcing steam into thebottom of said digester, and after the cooking process has proceeded for a predetermined time conveying the excess bisulphite liquor and sulphur dioxide gas from the upper part of said digester to a second digester at a relatively lower point therein, the second digester havwholly or partly filled with chips, then supplying the second digester from the bottom thereof with bisulphite liquor to a point adjacent to the point where the heated bisulphite liquor from the first digester is entering the second digester, the cooking process in the first-named digester being further advanced than in the second digester.

. 8. An apparatus for manufacturing wood pulp embodying a pair of digester tanks and a relief pipe leading from the upper portion of one tank to a relatively lower point on the other tank and substai'itially removed from the bottom thereof.

9. An apparatus for manufacturing wood pulp embodying a pair of digester tanks, a main relief pipe, a pipe leading from the upper portion of each of said digester tanks to said main relief pipe, other pipes leading from said main relief pipe' and connecting with each of said digester tanks at a relalively lower lever than said first-named pipes and at a substantial distance from the bottom of said digester tanks, and valves positioned in said pipes, whereby the excess bisnlphite liquor,,and sulphur dioxide gas from either one of said digester tanks may be conveyed to the other digester tank at a point relatively lower than that point on the first digester tank from which it was conveyed and substantially above the bottom of said digester tank to which it was conveyed.

In testimony whereof we have hereunto set our hands.

ELLIOTT R. BARKER. FRANCIS J. DOOLEY. 

